Honestly the idea was around long before it was being used for Germany and Spain. When the Italian Grand Prix went to Imola, it was while Monza was out of commission (in 1980 if I have the year right). After that, it was popular enough to be kept on the calender and they renamed it the San Marino Grand Prix. While this isn’t the same as the European Grand Prix, the concept is the same: one country, two grands prix, capitalizing on a large number of fans in one area.